1. Field of the Invention
The present invention relates to an ink-jet printer, and more particularly, to a method and an apparatus for inspecting errors of a home position in an ink-jet printer.
2. Description of the Related Art
Ink-jet printers perform a printing operation using a direct current (DC) motor. They generate information related to positions and a fire signal of a head using a sense signal output from an encoder sensor (not shown) installed behind a carriage (not shown). Here, the encoder sensor senses light irradiated from a light sensor (not shown) and then passing through an encoder strip having patterns in which black and white colors repeatedly appear, and generates a sense signal in a square wave shape at a level corresponding to the result of sensing. In this case, movement of the carriage, or works (processes) related to the carriage positions, are performed based on a home position information.
When power is initially applied to the ink-jet printers, they generate a sense signal while moving the carriage in a specific direction at a predetermined speed and convert the sense signal into a position. In this case, they recognize a position in which the carriage is not moved in a specific direction for a specific period of time, as an end position in a specific direction, which is the home position, and set the home position to an absolute position.
Hereinafter, in an ink-jet printer using a DC motor, a conventional method for calculating a carriage position using a sense signal will be described with reference to FIGS. 1A through 1C. FIG. 1A through FIG. 1C illustrate a conventional method for calculating a carriage position. FIG. 1A shows a waveform of a sense signal, FIG. 1B shows a waveform of a signal in which the sense signal is phase-transited by 90°, and FIG. 1C shows patterns of an encoder strip.
Counting of a position of a carriage starts at a rising edge of the sense signal shown in FIG. 1A. Thus, in the conventional method for calculating a carriage position, errors can occur in a calculated position according to the position of the carriage when the power is applied to the ink-jet printer carriage. For example, when the carriage is placed in positions 2, 3, and 4 of the encoder strip shown in FIG. 1C and these positions are set to absolute positions, counting of the position of the carriage starts in a position 5, which is a next rising edge of the sense signal shown in FIG. 1A. Therefore, for example, if an interval between black colors (or between white colors) is 1/150 inch and a unit of a position is 600 dots per inch (dpi) in the encoder strip, in the conventional method for calculating a carriage position, a maximum of 3/600 errors can occur according to a home position in which the carriage is not moved any more (i.e., an erroneous home position is calculated). Likewise, assuming that an alignment compensation value during a bi-directional printing operation is set using position information set when a power is initially applied to the ink-jet printer, if the ink-jet printer is turned off and then turned on, errors occur in a home position even though the alignment compensation value is stored, because the actual alignment compensation value would deviate from the set alignment compensation value during a bi-directional printing operation.